A leaf cell membrane is 5 µm thick. The diffusion coefficient for CO₂ in the cytoplasm is $D = 2.0 \times 10^{-5}\,\text{cm}^2\text{s}^{-1}$. The concentration difference across the membrane is $\Delta C = 1.5 \times 10^{-6}\,\text{mol cm}^{-3}$.

Using Fick's first law $J = -D\,\frac{\Delta C}{\Delta x}$, calculate the diffusive flux $J$ in $\mu\text{mol m}^{-2}\text{s}^{-1}$.

If the cell must import $800\,\mu\text{mol m}^{-2}\text{s}^{-1}$ of CO₂, determine whether diffusion alone can meet this requirement.

Question

A leaf cell membrane is 5 µm thick. The diffusion coefficient for CO₂ in the cytoplasm is $D = 2.0 \times 10^{-5}\,\text{cm}^2\text{s}^{-1}$. The concentration difference across the membrane is $\Delta C = 1.5 \times 10^{-6}\,\text{mol cm}^{-3}$.

Using Fick's first law $J = -D\,\frac{\Delta C}{\Delta x}$, calculate the diffusive flux $J$ in $\mu\text{mol m}^{-2}\text{s}^{-1}$.

If the cell must import $800\,\mu\text{mol m}^{-2}\text{s}^{-1}$ of CO₂, determine whether diffusion alone can meet this requirement.

Accepted Answer

Flux = 600 µmol m⁻² s⁻¹; diffusion alone is insufficient.

Igcse Model Questions Vol1 2021 Biology Question 38

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